A goal of data compression is to algorithmically process a block of input data of size X bits to produce a block of output data of size Y bits, where X>Y. The output block of data may then be more efficiently stored and transmitted. The compression operation maybe lossless or lossy, depending on the selected algorithm. Lossless data compression implies that the original data can be faithfully and exactly recovered after the compressed data is decompressed. Lossy compression is typically used for image data, where some amount of quality degradation can be tolerated in order to significantly reduce the bandwidth requirement to transmit the image data and/or the memory requirement to store the image data. Fundamental data compression algorithms include arithmetic coding, pulse code modulation, differential pulse code modulation, run-length coding, Shannon-Fano coding, Huffman coding, discrete cosine transform and various dictionary methods. The data compression ratio is determined by dividing the original amount of data by the amount that is obtained from the compression operation. The fundamentals of modem data compression were established by C. E. Shannon in “A Mathematical Theory of Communication”, The Bell System Technical Journal, Vol. 27, pp. 379-423, 623-656, July, October, 1948.
The use of data compression yields a number of benefits in modem cellular telecommunications systems, particularly in those that transmit and receive packet data such as in the General Packet Radio Service (GPRS). A first benefit is an improved radio usage efficiency, since fewer bits need to be transmitted over the air interface. A second benefit is a higher throughput performance, since fewer bits have to be transmitted, and therefore the probability of packet loss is reduced. This is particularly important for protocols such as the Transmission Control Protocol (TCP), where the loss of a packet may seriously degrade the throughput (e.g., the loss of a packet can result in a slow start). Another benefit is improved bandwidth usage on wireline links between the data compressor and the decompressor.
It is known in the prior art to provide some packet payload compression from attached proxies, especially for TCP applications. However, the proxy-based approach has the following drawbacks: (a) it adds a single point of failure; and (b) it lacks flexibility, as the data traffic is required to transit through the proxy.
For some specific applications, such as one known as the Session Initiated Protocol (SIP) that is operating through a Call Server Control Function (CSCF), the data packet payload compression/decompression is intended to be done through the CSCF. However, the use of this technique is essentially restricted to the application level, and thus does not provide a general widespread benefit.
It is also the case that some packet payload and/or header compression has been defined in the Radio Access Network (RAN) Packet Data Convergence Protocol (PDCP), or in the Serving GPRS Support Node (SGSN), specifically in a Sub-Network Dependent Convergence Protocol (SNDCP). However, these approaches require that specific negotiations occur between the mobile station (MS) and the wireless network, and do not provide the benefit of compression between the network compression/decompression point (RAN or SGSN) and the Gateway GPRS Support Node (GGSN). One drawback is that the packet data flowing through the IP network, i.e., between the SGSN and the GGSN, is not compressed, and thus greater bandwidth must be provided.
Existing GSM GPRS protocols offer payload compression by using V.42bis and V.44 standards, while existing UMTS GPRS protocols do not offer any payload compression
In some instances the use and/or specifics of data compression may be a proprietary wireless network feature and thus is not required to be standardized in the sense that normal network operation is standardized and applied by various manufacturers who make equipment for connecting to the wireless network. In this case it can be appreciated that the signaling or handshake exchange between the mobile station and the network must be accomplished in a way that enables the use of the proprietary feature, but without requiring that the signaling itself be the subject of standardization.
A proprietary feature normally cannot be implemented in a multi-vendor standardized environment, as it requires special proprietary signalling between elements (the Network Elements and/or the mobile station), and such signalling can cause errors if the intended recipient cannot interpret correctly the proprietary signalling.
In a strong competitive market, such as GPRS, the value added provided by a novel and/or useful proprietary feature can be a strong business differentiator. Thus, it would be desirable and important to provide an ability to implement such proprietary features, for example in the GPRS/UMTS standardized environment, without affecting correct operation and interoperability when interacting with network elements supplied by other vendors.